The present invention relates to tape cassettes.
Prior art techniques have provided tape cassettes which are equipped with a preventive slot on their bottom sides, which is covered with a snap cover, and which serves to prevent accidental erasures. With the snap removed, the slot causes a detector of associated tape recorder to operate, thus making the recording button thereof inoperative. In other words, a tape cassette, with its snap removed after recording thereon, inhibits duplicate recording, or erasing of such recording. This however, gives rise to the problem that the slot must be filled with something to function as the snap or the cassette itself must be replaced with a new one when it is desired to erase the recording from the tape or to re-cord thereon.
One prior art solution to this problem is an arrangement which permits the snap to be slid or turned over on a hinge. This again is impractical for chrome-bias tape or like cassettes in which the bias changeover slot is formed adjacent to the accidental erasure preventive slot, because the snap readily closes the bias changeover slot when it is slid or turned over. These prior art approaches will now be described in more detail by referring to the accompanying drawings.
FIGS. 1 and 2 schematically show the construction of one popularly known tape cassette having a bias changeover slot, in which a snap 1 is disposed to cover the opening of an accidental erasing preventive slot 2 being disposed adjacent to the bias changeover slot 3. The snap 1, as already indicated, is necessary for recording, but must be removed by detaching it from its base 4 when the recorded data is to be prevented from being erased by mistake. Without the snap 1, the miserasing or accidental erasure preventive slot 2 is open to a detection rod extended from a miserasing preventive device, e.g., a microswitch, installed in the associated tape recorder. When the detection rod enters the slot 2, the microswitch operates to make the recording button of the recorder inoperative. Hence, on a tape cassette with its snap removed, erasing cannot be effected but rather, only playback of the recorded cassette is available. When a tape recorder provided with an automatic chrome-bias changeover mechanism is used, the bias changeover slot is open to the bias changeover mechanism of the recorder, permitting chrome-bias recording to start automatically.
As described above, tape cassettes of the type having no bias changeover slot involve certain difficulties once the snap is detached. Prior art techniques have proposed the following improvements on this type of tape cassette. With reference to FIG. 3, a schematic plan view is shown to illustrate part of a tape cassette in which a plastic plate 5 is used instead of the snap. The plate 5 is moved in the direction of an arrow 6, i.e., toward the center of the cassette after recording, whereby the accidental erasure preventive slot is opened.
Another prior art improvement is schematically shown in FIGS. 4 and 5, in which a plastic plate 7 pivotably mounted on a hinge 8 is used instead of the conventional snap. The hinge 8 is held in a column 9 formed with a case body 11. The accidental erasure preventive slot 12 can thus be opened by pivoting the plate 7 in the direction indicated by arrow 10, i.e., toward the center of the case 11. The plate 7 is turned over and fitted to the case 11.
These prior art arrangements, however, cannot be utilized for tape cassettes of the type equipped with the bias changeover slot, because the plate 5 or 7 necessarily covers the bias changeover slot when it is slid or turned over to open the accidental erasure preventive slot.
Yet another prior art solution to the problem is the use of a plug instead of the snap, which can be pulled out to open the slot and set into position to close it, when necessary, as in digital tape cassettes. This construction, however, poses another problem in that the plug is very likely to be lost once it is removed.